1. Field of the Invention
The present invention relates to a system and method for modifying the refractive error in the live cornea of an eye. More particularly, the present invention relates to a system and method for modifying the live cornea by separating an internal area of the live cornea into first and second opposed internal surfaces, forming a corneal flap, positioning an implant having a predetermined refractive portion on one of the internal surfaces and holding the implant adjacent thereto using a ring-shaped instrument, and then ablating the implant using a light emitting device and replacing the corneal flap over the ablated implant.
2. Description of the Related Art
A conventional method for correcting the refractive error in a cornea is known as keratophakia, which involves implantation of a lens inside the cornea. Keratophakia uses an implant, which is placed into the cornea approximately equidistant from the exterior surface of the cornea and the interior surface. The procedure is usually done by first preparing a lens from corneal donor tissue or from synthetic material using a cryo-lathe. The lens is implanted by removing a portion of the cornea with a device called a microkeratomes, and the tissue is sutured back into place over the lens. However, there can be problems when microkeratomies are used for cutting the cornea. First, irregular keratectomies or perforations of the eye can result. Second, the recovery of vision can be rather prolonged.
Another surgical technique exists that uses a femtosecond laser to separate layers inside the stromal at least two-thirds of the distance from the top surface of the cornea to the inside of the eye. An incision is made to access this area, and a solid inlay is inserted to help correct myopia in the eye. However, separating the layers in the bottom two-thirds of the stromal makes it difficult to access the separated area to insert the inlay, and virtually impossible to change or modify the inlay without another extensive surgical procedure. This procedure also requires making an incision, which is parallel to the visual axis and is limited in the lateral direction by a maximum size of 0.3 mm to encase a relatively rigid inlay that forces the tissue in the lateral direction.
A further surgical technique exists that forms a flap-like portion of the live cornea, which is removed to expose an inner surface of the cornea. A blank is positioned on the exposed inner surface of the cornea, and a laser beam is then directed onto certain portions of the blank based on the type of ametropic condition (i.e., myopia, hyperopia or astigmatism) of the eye, so that the laser beam ablates those portions and thus reshapes the blank. The laser beam can also be directed onto certain portions of the exposed surface of the cornea to ablate those surfaces of the cornea. The flap-like portion of the cornea is repositioned over the remaining portion of the blank, so that the remaining portion of the blank influences the shape of the reattached flap-like portion of the cornea and thus modifies the curvature of the cornea. A more detailed description of this procedure is described in U.S. Pat. No. 5,919,185 to Peyman, the content of which is herein incorporated by reference.
Although this technique is very successful, this type of procedure may require ablation of a large portion of the blank, which results in the dispersion of a relatively large amount of heat. This heat can cause the lens to shrink and thus possibly inadvertently alter the intended refractive properties of the cornea, in which event correction will be less than desired or even irregular.
Additional surgical techniques exist that use ultraviolet light and short wavelength lasers to modify the shape of the cornea. For example, excimer lasers, such as those described in U.S. Pat. No. 4,840,175 to Peyman, the entire content of which is incorporated by reference herein, emit pulsed ultraviolet radiation that can be used to decompose or photoablate tissue in the live cornea to reshape the cornea. This technique is commonly known as the laser surgical technique known as laser in situ keratomycosis (LASIK).
In the LASIK technique, a portion of the front of the live cornea can be cut away in the form of a flap having a thickness of about 160 microns. This cut portion is removed from the live cornea to expose an inner surface of the cornea. A laser beam is then directed onto the exposed inner surface to ablate a desired amount of the inner surface up to 150-180 microns deep. The cut portion is reattached over the ablated portion of the cornea and assumes a shape substantially conforming to that of the ablated portion.
However, because only certain amount of cornea can be ablated without the remaining cornea becoming unstable or experiencing outbulging (eklasisa), this technique is not especially effective in correcting very high myopia. That is, a typical cornea is on average about 500 microns thick. The laser ablation technique requires that at least about 250 microns of the corneal stroma remain after the ablation is completed so that instability and outbulging do not occur.
Additional methods for correcting the refractive error in the eye include inserting an implant in-between layers of the cornea. Generally, this is achieved using several different methods. One method involves inserting a ring between layers of the cornea, as described in U.S. Pat. No. 5,405,384 to Silvestrini. Typically, a dissector is inserted in the cornea and forms a channel therein. Once it is removed, a ring is then inserted into the channel to alter the curvature of the cornea. In another method, a flap can be created similarly to the LASIK procedure and a lens can be inserted under the flap, as described in U.S. Pat. No. 5,722,971 to Peyman. A further method involves forming a pocket using an instrument, and inserting an implant into the pocket, as described in U.S. Pat. No. 4,655,774 to Choyce. The entire contents of each of these three patents are incorporated herein by reference.
However, with the above-described techniques, a knife or other mechanical instrument is generally used to form the channel, flap or pocket. Use of these instruments may result in damage or imprecision in the cut or formation of the desired area in which the implant is placed.
Therefore, there exists a need for an improved method of correcting refractive error in the cornea of an eye.
Accordingly, a primary object of the present invention is to provide a method for modifying the cornea of an eye without experiencing the drawbacks associated with the known techniques discussed above, to thus correct severe ametropic conditions.
A further object of the present invention is to provide a method for modifying the cornea of an eye by using a device that can be placed on the surface of the live cornea and reshaped thereon.
Still a further object of the present invention is to provide a method for modifying the cornea of an eye by removing a layer of the live cornea to expose a surface underneath, then placing an implant with predetermined refractive properties on the exposed surface, which can be reshaped while on the exposed surface.
Yet another object of the present invention is to provide a method for modifying the cornea of an eye wherein the implant can be held adjacent to the exposed surface of the cornea using an instrument during ablation thereof.
Yet another object of the present invention is to provide a method for modifying the cornea of an eye that allows for corrective measures that avoid or eliminate outbulging or instability in the cornea.
The foregoing and other objects are substantially attained by a method of correcting the refractive error in a cornea of an eye, including the steps of forming a flap in the surface of the cornea, moving the flap to expose first and second internal surfaces of the cornea, positioning an implant adjacent the first internal surface, with at least a portion of the implant having refractive properties, holding the implant adjacent the first internal surface using a tool, ablating at least a portion of said implant with a light emitting device when said implant is held in place by the tool on the first exposed surface of the cornea, and repositioning the flap over the implant.
The foregoing objects of the present invention are further attained by a method of correcting the refractive error in a cornea of an eye, including the steps of separating a portion of the surface of the cornea into first and second internal surfaces to form a corneal layer, the first surface facing in an anterior direction of the eye and the second surface facing in a posterior direction of the eye, moving the corneal layer to expose the first internal surface, positioning a lens on the first internal surface, holding the lens stationary relative to the first internal surface using an instrument, ablating at least a portion of the lens using a laser when said lens is being held by said instrument, and moving the corneal layer so that the second internal surface substantially overlies the lens.
Other objects, advantages, and novel salient features of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention.